使用以下KoreaEx数据：重命名列并收集国家，年份和出口。再次重命名列以正确标记Month和Exports，然后尝试group_by并汇总但NA返回。是不能识别的数值，代码是不正确的？
> head(KoreaEx)
CTYNAME year EJAN EFEB EMAR EAPR EMAY EJUN EJUL EAUG ESEP EOCT ENOV EDEC
9 Korea, South 2009 1,807 2,074 1,835 2,024 2,474 2,295 2,372 2,642 2,711 2,842 2,797 2,739
27 Korea, South 2010 2,977 3,073 3,350 3,157 3,291 3,230 3,372 3,146 3,161 3,309 3,384 3,370
45 Korea, South 2011 3,507 3,146 3,520 3,861 3,881 3,490 3,626 3,785 3,569 3,471 3,820 3,785
63 Korea, South 2012 3,472 4,103 3,700 3,666 3,494 3,589 3,516 3,132 3,585 3,512 3,195 3,318
81 Korea, South 2013 3,389 3,521 3,413 3,162 3,270 3,446 3,470 3,439 3,164 3,582 4,040 3,789
99 Korea, South 2014 3,712 3,617 3,830 3,811 3,683 3,767 3,670 3,801 3,644 3,604 3,680 3,654
colnames(KoreaEx) = c("Country", "Year", "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
KoreaEx = KoreaEx %>% gather(Country, Year, Jan:Dec)
colnames(KoreaEx) = c("Country", "Year", "Month", "Exports")
> head(KoreaEx)
Country Year Month Exports
1 Korea, South 2009 Jan 1,807
2 Korea, South 2010 Jan 2,977
3 Korea, South 2011 Jan 3,507
4 Korea, South 2012 Jan 3,472
5 Korea, South 2013 Jan 3,389
6 Korea, South 2014 Jan 3,712
KorExp %>% group_by(Year) %>% summarise(Exports = sum(Exports, na.rm = FALSE))
Exports
1 NA
> 2:#1